Skull of the neotenic salamandrid amphibianTriturus alpestris and abbreviated development in the Tertiary Salamandridae
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Abstract:
The skull of neotenic individuals of the Alpine Newt Triturus alpestris from the locality Drakolimni (Greece) is described on the basis of models made from magnified serial frontal sections. In order to recognize features associated with neoteny and paedomorphosis, the results were compared with normal development of contemporary Triturus and of other Caudata. The neotenic larvae from Greece correspond to advanced stages of metamorphosis in normal development of Triturus alpestris. Comparison with salamandrids from the Tertiary of Europe in which the hyobranchial skeleton was preserved, namely Brachycormus noachicus, Chelotriton paradoxus, and Palaeopleurodeles hauffi, revealed that both latter taxa were completely metamorphosed adults anatomically similar to their contemporary relatives Tylototriton, Echinotriton, and Pleurodeles, whereas Brachycormus, though apparently related to Chelotriton, was a neotenic amphibian. This is suggested by its incompletely metamorphosed but ossified hyobranchial skeleton. © 1996 Wiley-Liss, Inc.Keywords:
Neoteny
Salamandridae
Triturus
Pleurodeles
Heterochrony
One of the most interesting heterochronic processes in the European newt (genus Triturus) is paedomorphosis, a phenomenon of attaining reproductive maturity while retaining larval features. However, paedomorphosis seems to be rare in the crested newt (Triturus cristatus superspecies). In the locality Vrba, near the town of Tuzi (Montenegro), Dr Georg Džukić found paedomorphic Macedonian crested newt (Triturus macedonicus). In this paper, new evidence for this heterochronic process in the crested newt from Montenegro is reported.
Neoteny
Triturus
Macedonian
Montenegro
Heterochrony
Salamandridae
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Evolutionary theory assumes that facultative paedomorphosis in newts and salamanders is adaptive in allowing either a younger age at maturity or resource partitioning between the heterochronic morphs. In newt populations that only take the metamorphic ontogenetic pathway, juveniles are terrestrial and avoid food competition with larvae and breeding adults. In contrast, in populations where paedomorphosis occurs, branchiate newts of all sizes coexist in the aquatic habitats, posing the question of whether intramorph competition exists and its relationship with the evolution of paedomorphosis. We studied size-related predation in such a size-structured community of branchiate Alpine newts (Triturus alpestris) inhabiting a deep alpine lake. Although gape limitation may explain such size-related predation, individuals also exhibited selectivity according to prey size. Amongst small prey that were within the capture range of all newt size classes, smaller newts preyed on smaller items than did larger ones. We assume that such decisions favour the coexistence of different-sized individuals. It is suspected that such size-selective predation on items which are avoided by water-living metamorphs allows the maintenance of facultative paedomorphosis, in favouring resource partitioning between morphs.
Neoteny
Heterochrony
Salamandridae
Triturus
Facultative
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The skull of neotenic individuals of the Alpine Newt Triturus alpestris from the locality Drakolimni (Greece) is described on the basis of models made from magnified serial frontal sections. In order to recognize features associated with neoteny and paedomorphosis, the results were compared with normal development of contemporary Triturus and of other Caudata. The neotenic larvae from Greece correspond to advanced stages of metamorphosis in normal development of Triturus alpestris. Comparison with salamandrids from the Tertiary of Europe in which the hyobranchial skeleton was preserved, namely Brachycormus noachicus, Chelotriton paradoxus, and Palaeopleurodeles hauffi, revealed that both latter taxa were completely metamorphosed adults anatomically similar to their contemporary relatives Tylototriton, Echinotriton, and Pleurodeles, whereas Brachycormus, though apparently related to Chelotriton, was a neotenic amphibian. This is suggested by its incompletely metamorphosed but ossified hyobranchial skeleton. © 1996 Wiley-Liss, Inc.
Neoteny
Salamandridae
Triturus
Pleurodeles
Heterochrony
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Abstract We report the occurrence of facultative paedomorphosis in the three species of newts (Pleurodeles waltl, Lissotriton boscai and Triturus pygmaeus) from dry and seasonal Mediterranean areas from southern Spain. These are the first records of paedomorphosis for P. waltl and L. boscai, and the second for T. pygmaeus. Other than the previous T. pygmaeus record, these are the first observations of paedomorphosis in the southern half of the Iberian Peninsula. Most of specimens demonstrating paedomorphosis live in artificially permanent aquatic environments. Nevertheless, a paedomorphic individual of L. boscai was found in a natural yearly temporary brook that held water during the previous two years. Paedomorphs are at low frequency in most cases. However, a single isolated population of P. waltl is probably composed entirely of paedomorphs.
Neoteny
Salamandridae
Pleurodeles
Triturus
Facultative
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Triturus
Heterochrony
Salamandridae
Rejuvenation
Notophthalmus viridescens
Neoteny
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Current evolutionary models suggest that the presence of heterogeneous habitats favours the evolu- tion of polymorphisms. In such cases, alternative phenotypes can coexist because they use different resources. Fac- ultative paedomorphosis is a heterochronic polymorphism in which a morph - the paedomorph - retains larval traits during the adult stage while the other morph - the metamorph - is fully metamorphosed. The aim of this study was to determine the microhabitat use and the diet of Alpine newt paedomorphs, metamorphs and immatures ( Triturus alpestris apuanus) coexisting in a small pond in Tuscany, central Italy, i.e. in a habitat where dimorphism is not expected. Although the two adult morphs do not use exactly the same resources, resource partitioning was weaker than in deep Alpine lakes. Nevertheless, the diet of immature gilled newts (larvae) differed from that of adults (met- amorphs and paedomorphs). While the larvae eat a large number of planktonic organisms, the adults focus on insect larvae and newt eggs. The differences in resource use favour the coexistence of aquatic juveniles and adults. In the studied pond, facultative paedomorphosis was previously shown to be favoured by a precocious maturity of the paedomorphs. This study shows that the coexistence of paedomorphs and metamorphs may also be supported by some dietary and spatial segregation, although any advantages gained by this pattern are rather limited in the adult stage.
Neoteny
Triturus
Salamandridae
Heterochrony
Facultative
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Current theories on the evolution of paedomorphosis suppose that several ontogenetic pathways have appeared according to different selective pressures. The aim of this study was to find out whether two distinct processes can lead to paedomorphosis in the Alpine newt, Triturus alpestris. In this respect, we compared age structures of paedomorphic and metamorphic individuals in two newt populations where the two forms lived syntopically. Whereas paedomorphosis resulted in a slower rate of somatic development in one population, it resulted in an acceleration of sexual maturation in the other population. These processes correspond to neoteny and progenesis, respectively. These results suggest that phenotypic plasticity can result from contrasted ontogenetic pathways between two populations of the same species. They give support to models that consider gonadic development as the target of selection under different environmental pressures.
Neoteny
Triturus
Heterochrony
Salamandridae
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Neoteny
Triturus
Salamandridae
Facultative
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Neoteny is common in some populations of Palmate newts Triturus helveticus of Southern France. Population samples have been collected from 117 pools, at three different seasons of the year. Percentages of neotenic individuals have been calculated for 29 of these pools where neotenic newts were found. Neoteny is not evenly distributed over the whole study area. It is more prevalent in the S.E. part of the Causse du Larzac and in the Causse de Blandas, than in the coastal plains of Languedoc. On the “causses” (arid limestone tablelands), neoteny only occurs among palmate newts, no neotenic individual having ever been found among the sympatric Triturus marmoratus population. Morphological differences between neotenic and normal populations of Triturus helveticus are described. None of them is consistent enough to allow sub-specific status to be given to the neotenic population. Breeding takes place later in the season among the Larzac population and the duration of the aquatic phase of the yearly cycle is also longer in the plateau population than among the newts of the coastal plains. All these differences, morphological as well as biological, disappear when the newts are kept in laboratory conditions. Metamorphosis occurs normally when the progeny of both newt populations are bred in the laboratory. However mortality is much higher among the progeny of neotenic females, during their first three months of life.
Neoteny
Salamandridae
Triturus
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Facultative paedomorphosis occurs rarely in the genus Triturus compared to other European newts such as Ichthyosaura alpestris and Lissotriton spp., with most of observation related to single or few individuals per site. In this paper we report about body size, age and population size of two populations of Triturus carnifex with paedomorphs. Since one of the populations consisted of approximately 25% of paedomorphs, this is the first study about a population of large-bodied newts with a conspicuous number of paedomorphic individuals. We found evidences for an ecological causation of paedomorphosis, as well as further support for two recent findings about paedomorphosis: the reduction of sexual size dimorphism and the female-biased sex-ratio within paedomorphs.
Neoteny
Salamandridae
Triturus
Facultative
Sexual dimorphism
Heterochrony
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